This is my first post (been lurking for a while) but PFD use is kind of a hot button with me and since I use both inflatable and regular PFD's, I wanted to offer my perspective on when I wear one versus the other.
I've been running rivers for about 30 years in canoes, kayaks and rafts and I never get on the water in a small craft without a PFD (and yes, I can swim and even teach kayaking). I strongly agree with the others that one should use a regular PFD for whitewater, not an inflatable. However, flat and mild water are another thing. Most of the time, I fish rivers that are class I, maybe 2-, like the Stilly, Snohomish, lower Yak canyon, etc. I rarely observe anyone wearing a PFD on these types of rivers. On lakes and in the salt, it's even rarer. An inflatable has drawbacks, but IMO it's far better than wearing none at all, especially while wearing waders. I know plenty of people who have developed serious leaks, holes or faulty vavles while on the water in their float tubes or pontoon boats.
So what to do? I've used my kayaking PFD on lakes and rivers and truthfully even the lowest profile ones are a pain to wear while fishing. I've tried wearing a vest or lanyard over it - way too bulky, so I take it off each time I stop to fish - big pain. Tempted to join the masses and store mine on the back deck, I finally bought an inflatable because of it's one main advantage - I'll wear it. I bought the manual inflation type and I bought one that is integrated in to a fishing vest (by Stearns). It's more comfortable than some of the suspender-type. It's not the most attractive fishing vest in the world but I find I leave it on the whole day. A PFD not worn is useless.
As I said though, in whitewater, I wear a normal kayaking Type 3 PFD for a few other reasons in addition to not being able to pull the cord. If you buy an inflatable, be aware of some of the other drawbacks and use good judgement in wearing it. Most inflatables have high bouyancy and float you face up, a good thing most of the time. But they are nearly impossible to swim in which is bad if you find yourself having to swim aggressively away from a sweeper. Almost all of the floatation is in the front making climbing back in a boat or getting on/over a sweeper all but impossible. Unlike a normal PFD, you can't safely wear a jacket, vest or chest pack over the top of it. If it can't expand outwardly, it will put so much pressure on your chest, you'll likely suffocate. The cartridges are a one-time use, so you'll need to carry spares. The little green pin is very fragile and after breaking several spares, I keep my spares in a small pill container. I regularly inflate mine by mouth to check for proper inflation and leaks and then reposition the yellow pull cord as high as possible to maximize it's visability. Even with these precautions, I still wouldn't rely on it's or my performance in whiterwater.
So if you'll mostly be using your boat on flat or mild water, be honest with yourself & ask - "Will I really wear a PFD or will I get complaicent once I get comfortable with the boat?". If you're like most people and are likely not to wear one, consider an inflatable for the gentle waters - it's better than nothing. They aren't cheap but I'm sure your loved ones would gladly chip in!
If you think you'll wear a normal PFD and/or will do whitewater, everyone is right - get a good, comfortable kayaking PFD. They are cut with larger arm holes than most rafting PFD's and often have more adjustment straps for a better fit. Mail order is great for somethings but like shoes, you want to try them on; what's comfortable on one person isn't on another. They're all comfortable when worn loosely but cinch it down tightly, then cinch it some more - you'll find out why the first time you swim. A good tightness test: with arms over your head, someone should be able to pick you up from the ground by the shoulder straps without it riding up past your ears. Move around in it, pretend you're casting or rowing. Take time to try on several and get which ever is the most comfortable - things like pockets and color should be secondary. However, if you wear waders in your boat try to get one with a lash tab, you'll want to keep a river knife handy. You'll probably find the best selection of kayaking vests at kayak shops like Northwest Outdoor Center, Pacific Water Sports or REI in Seattle. They're not cheap but neither's your life.
Hope this helps. Just remember, like a wading belt, the best type of PFD is the one being worn.